The present invention relates generally to the field of data recall in a hierarchical storage management system, and more particularly to recalling data objects stored on secondary storage media such as tapes or removable disks.
A hierarchical storage management (HSM) system stores frequently accessed data on a higher tier comprising fast storage devices (for instance, flash or hard disk drives), and migrates less-frequently accessed data to a lower tier comprising slower, lower-cost storage (such as tape cartridges in a tape library), to lessen the total cost of data storage. The HSM system may recall migrated data to a higher tier when access to the data is requested. In an HSM system, data that has been migrated to a lower tier is referred to as having been migrated (or as being in a migrated state). Migrated data that has been brought back up to a higher tier is “recalled” (sometimes referred to as being in a “resident” state).
Tape libraries are often used for storing for vast amounts of data, due to a cost advantage (per unit of storage) provided by tape storage over some other storage types. Some storage systems are shared by a plurality of users and/or teams. In such an environment, multiple users are likely to perform write/read operations on a shared tape storage library system at the same time. In some tape libraries, users may be assigned reserved time-slots. During a reserved time-slot, recall requests associated with the corresponding user are given high priority for processing.